Frequency controlling and regulating means for oscillating elements



Apnl 2, 1957 c. F. CLIFFORD 2,787,115

FREQUENCY CONTROLLING AND REGULATING MEANS FOR oscILLA'rING ELEMENTS Flled March 11, 1952 2 Sheets-Sheet 1 April 2, 1957 c. F. CLIFFORD FREQUENCY CONTROLLING AND REGULATING MEANS FOR OSCILLATING ELEMENTS 2 Sheets-$heet 2 Filed March 11, 1952 INVENTOR C. a. clay m4 w M m wxnya.

United States Patent FREQUENGY CONTRGIZLING' AND REGULATING MEANS FOR? USCI'LLATING ELEMENTS" This invention relates. tofrequency controlling and regulating means for oscillating. elements, such as the I oscillator of a time piece, in'which'a relatively high degree of isochronism is important.

One factor which controls the frequency of an oscillator is, the returning, force and=mostregulators operate on the principle of varying such force, increasing itfor faster oscillations and. decreasing it for slower oscillations. The regulator engaging the hair spring of a balance wheel, byshortening or lengthening the eifective length of spring operates-in such manner. Where ahigh degree of isochronism is required; care must be taken that any regulating. device does notcause the returning force to depart unduly from the isochronous requirement that there shall be a substantially direct linealrelationbetween the returning. force and the amplitude of displacement of the oscillator, and. the known example" of: regulator above described,. substantially satisfies thisrequirement;

Magnetic. escapements have recently been'developedlin which the. oscillator is a permanently magnetised mem ber carried?v by a reed the resilience of: which provides the major portion of thereturning. force, themagnitude of, which determines. the frequency of oscillation, but the known regulator mechanism; above-described, is not practical for. application to such type of oscillator. For such type of oscillator it. has'been proposed to provide a screw. of. magnetic material with itsend within the field of such magnet and. its I axis on. but transverseto the" axis ofrepose of .the oscillator,.turning.of thescrew bringing more or less of such end into the field of the'magnet or bringing such and closer to or awayfrom the magnet and-thereby applying. an adjustable magnetic returning force to. the. oscillator supplemental to the resilient re-' turningforce of. the reed. and many small force transmitted throughthe magnetic. lockaof the magnetic escapementas is necessary for impulsing the oscillator. Such magneticregulationhas the disadvantagethab it. has an adverse efiecton the isochronism of the oscillatontbecause at the smaller amplitudesofl oscillationthe'magnet pole of 'the oscillator isunder theinfluence of such-regulating screw for a larger proportion of its stroke than it is at the larger amplitudes,- the latter being, therefore; lower in frequency. Relative. to. the amplitude ofi oscillationof the magnet and togive afrequency variation'of a reasonable order for the. purpose of aregulator using. a screw of' practical. diameter and. proximity, an. isochronous error is unavoidably introduced which' over the: range of adjustmentas explainedlaten is substantially ofthe same order as the regulation which it. provides. Such construction. of regulator can. hardly therefore be. described as satisfactory.v

It has also been proposed, in. a. timepiece having, a mechanical escapement, to replace the usual spring. or gravity returning force for the oscillatingel ement by a magnetic returning force, in one example the oscillator including a bar magnet having its end: presented tothe endo'f a magnetised screw of opposite polarity, the proxiinity of'which is adjustable by turning the screw.

2,737,115 Patented Apr. 2, 19.57

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Obviously, such an arrangement would have the disadvantagefound to exist with the regulating screw above described, but such disadvantage of isochronous. error would be far greater because of the departure ofthe" re turningforce from the requisite condition of linear functionrelative to the amplitude of deflection, which de parture would apply to the whole returning force and not just to a small fraction thereof as in the case of an adjustable superimposed small' regulating; force. In an alterna; tive example of the substituted magnetic returning force, the oscillator includes a short pieceof channel or C shaped magnet complementary to a longer piece of channel or C-shaped magnet, arranged at right angles to and symmetrically of the arcuate path ofmovement of the oscillat ing magnet; In addition to such main longer channel magnetthere were provided repelling, (i-shaped. magnets located at each side of the arc of movement of the oscillating magnet. It can be deduced. from the isochronous errors of our own device, which can be effective though only on 1% of the returning force, that variation of the returningv force from the main longer channel magnet causingthe isochronous error, maybe anything from 5% to 20% of the whole returning force. Consequently for this reason alone the construction has an error factor which is impractical for a timepiece, but the provision of the repelling C-shaped magnets introduces a returning force having a square law error, which would be even less practical for a timepiece owing to the isochronous error thereby introduced;

The object of the present invention is an improved magnetic regulating device capable of providing a practical range of frequency regulation without introducing an. isochronous-error of relatively impractical'magnitude.

The present invention is, based upon an appreciation of the fact that the isochronous error factor may be completely negligible when resulting from a magnetic force. not beingv the main restoring force but of sufficient magnitude to provide a useful range of regulation and obtaining. from a magnetic coupling between one part having an arcuate path ofmovement and a complementary part symmetrically tangential thereto, suitably divergent therefromand o'f suflicient width relative to the run" amplitude of the arc of oscillation, with adjustment for proximity. Such regulating means provides an adjustable returning force of eifective magnitude supplemental to a main returning force so that the non linear variation of such supplemental force (throughout the amplitude of. oscillation and causingv error of isochronism), though substantial relative to the whole supplementary returning force,.is completely negligible in relation to the. basically'linear characteristic of" a much larger total returning force. Therefore the construction is well within the practical. limits. for a timepiece.

According to the invention a magnetic frequency regulator for an oscillatingrnass, havinganon-magnetic main restoring force givingsuch mass a natural frequency of oscillation, of the kind. comprisingcomplementary parts inter-acting. magnetically to provide a modified. total: restoringforceby. addingto or subtracting from themain restoring force,oneof said parts being mounted tomove with the" oscillating mass, one of saidparts. being, shaped to present to'the other part arel-atively divergent surface symmetrically.- throughout the amplitude. of oscillation, mount-ingmeans for supporting the non-oscillating part, and adjustable means for said'mounting means for varying the effective proximity of the said. divergent surface to the other part,,is. characterised in that the said divergent surface has its divergent. dimension atleast equal to half the normal amplitudeofoscillation-and its radiusof curvature not less than the normal maximum amplitude of oscillation.

According to one embodiment of the invention as applied to a magnetic escapement having a vibrating magnet a substantially flat strip of magnetisable material thinner than the magnet is presented symmetrically to the magnet pole (or poles) and is of width in the direction of oscillation appreciably in excess of the locus of the magnet projections upon it while oscillating at maximumamphtude. Mechanimal means are provided for adjusting the proximity of this fiat plane relative to the magnet in order to regulate the frequency. Such movement should preferably be rectilinear along the axis but it is found that no harmful secondary effects occur if motion round a fairly large radius is substituted. With this arrangement a regulating force representing only 2% of the total returning force is capable of providing a time regulation of up to 1% or 14.4 minutes per day and the maximum measurable error of isochronism even when the plate is within .005 of the vibrating magnet is negligible within ordinary practical requirements of an ordinary timeplece,

being within the order of less than half a minute a day,

or about 0.035%.

The example above described of a flat strip of magnetic material is a convenient embodiment but the flat end of a screw if of large enough diameter could be made to work, but it will be appreciated that the diameter of the screw would have to be so large as to come within the bounds of the impractical, bearing in mind that the circular shape of the end area, unless very large, must aggravate the isochronous errors of the resultant restoring force.

Although spring steel works quite well (with quite small losses), for the best effects the fiat strip of magnetic material should be made of a low loss alloy such as the nickel irons.

In order to reduce the isochronous error of the resultant restoring force to within even smaller proportions than that obtainable even with the flat plate embodiment above described it is herein proposed to vary the width of the regulating plate, making it narrower at the axis of symmetry and/or possibly by giving it a slight curvature i. e. so that the plate is not quite fiat.

As a further modification, and in order to counteract the square law effect upon the adjustment of the regulator plate, cam means are provided whereby movement of the regulator plate relative to an adjusting member follows compensating square law giving less movement to the plate per unit of movement of the adjusting member as the plate approaches the oscillator magnet. By this means it becomes possible to calibrate the movement of the adjusting member for a given variation of the timing, say in minutes per day.

In the accompanying drawings:

Fig. l is a perspective view showing the essential parts of a magnetic escapement for a timepiece embodying one example of the present invention;

Fig. 2 is a fragmentary view showing another example of the present invention;

Figs. 3, 4 and 4A are fragmentary views showing modifications of the construction shown in Fig. 1;

Fig. 5 is a detail dimensioned View of the magnet.

As shown in Fig. 1, on the base unit a is a train of gears consisting of gear pinions b and c driving a spoked mag netic escape wheel a complementary to an oscillator assembly consisting of a magnet e mounted on a spring reed f secured by small screws g to the magnet and by a fixing screw it to a lug h on the base unit. The outer pivot for the spindle of the escape wheel d is carried by a bracket i on which bracket and concentrically with which wheel is pivotally mounted a regulating lever j formed with a cam Fixed to the bracket i is one end of a spring m to the other end of which is fixed a flat plate It. A lug n on the spring m acts as a follower to the cam 1' A rider e is shown slidably mounted on the outer arm of the magnet e and provides rough adjustment for frequency regulation.

In the example of the invention shown in Fig. 1 the essential features and dimensions of the mechanism are as follows:

The oscillating mass consisting of the magnet e, spring 1 and securing screws g is 0.34 gram and the rider e is .02 gram. The mass is designed to oscillate vibrations per second and the centralising force from the spring at 0.75 mm. deflection, which is approximately the normal defiectionabout 5 grs./cms. The magnet e is made from metal known under the registered trademark Vicalloy to the dimensions shown in Fig. 5, and is magnetised to maximum strength. The escape wheel d is made of metal known under the registered trademark Mumetal and of 0.25 mm. thickness. The regulating plate It is of 0.25 mm. thickness also of Mumetal and is 3 mm. in width, and is flat, being positioned so that its end is the same distance from the face of the escape wheel d as the adjacent end of the magnet. The adjusting cam j is proportioned to provide movement to vary the distance between the end of the magnet and the face of the plate from a minimum of 0.1 mm. and maximum of .5 mm. and it is intended that normal time-keeping shall be obtained with the plate distance of about 0.4 mm. Tests carried out of the above construction shoed that no error of isochronism could be attributed to change of position of the regulating plate over a variation of power input from between 5 to 12.5 grams/cms. per minute, and variation of 0.5% frequency was achieved. The length of the regulator plate, out to its supporting spring m was greater than the length of the adjacent magnet pole for obvious mechanical reasons but the outer portion of such length is clearly relatively ineffectual as regards the frequency of oscillation of the magnet.

In the example shown in Fig. 2, the same oscillating magnet assembly and escape wheel is incorporated and its parts given the same reference characters. The regulator consists of a bent plate 0 having its end 0 of the same size as the plate n of Fig. 1 and approximately 0.15 mm. from the end of the magnet pole throughout its substantially lineal adjustment by means of the screw p. Adjustment is approximately 4 mm. from a full in position with the end of the plate level with the end of the magnet pole. Substantially 0.4% frequency regulation was obtainable by this construction. The bent plate 0 is of the same metal as the plate n. As with the constinction of Fig. 1 no measurable error of isochronism could be attributed to the presence of the end 0 of the regulator.

Comparing such results with a previously known method using a screw such as p positioned substantially in place of the regulating plate 0 with the nearest point on its side 0.15 mm. from the end of the magnet pole, the frequency adjustment obtainable was about 1.0% but it introduced an error of isochronism which, with the screw in its position of maximum effect, amounted to 1% over a power input range of 5.0 to 12.5 grams cm. per minute. The isochronism error is thus of substantially the same order as the frequency adjustment which it provided.

In the modification shown in Fig. 3, the regulating plate n though otherwise the same as the plate n of Fig. 1 has a radius of curvature of 12 mm. and its cooperating end face being substantially of the same dimensions as that of Fig. 1 is convex to the magnet pole. With this modification the possible frequency variation was increased from 0.5 to 0.75% and still without any measurable adverse effect on isochronism.

As shown in Fig. 4, an alternative end plate 12 has its effective face presented to the magnet proportionally varied by the formation of a hole n as shown. This hole is expected to give correction for isochronous error of 0.25% over the same torque range should such correction be required. Obviously other shaping or embossing or indenting could be used to achieve the same object. For example, as shown in Fig. 4A the end of the plate q is notched at q giving awaisted effect which can similarly Ive-proportioned and used to give the required c'or-' rection of isochronous error.

While it is appreciated that'movement of n or o -has an angular component, this in practice is so small as to have no noticeable effect.

A further object of the invention is a simple and improved means for correcting errors of isochronism. Thus, instead of providing relative proximity adjustment for the magnetically interacting parts, the proximity may be predetermined. The arrangement for example of Fig. 4 or' Fig. 4A may be used to correct normal errors of isochronism in an oscillator in which a spring provides the restoring forceand in which, as is well known, an iso* chronous error exists, the oscillations for the larger amplitudes being slower than for the'smaller amplitudes. The shaping and disposition of the magnetically interacting parts would therefore be such as to provide a proportionally over-increased restoring force towards the ends of the amplitude of oscillation, thus speeding up the movement at such positions and compensating for the said known' isochronous errors.

The invention is obviously not limited to the example which shows parts of a spring driven escapement for a timepiece, asit' can be used for a frequency compensator or regulator for oscillators impulsed' electromagnetically or electrostatically instead of through a mechanically driven escapement wheel.

What I claim is:

i. A magnetic frequency regulator for an oscillating mass, having a nonemagnetic main restoring force giving such mass a natural frequency of oscillation which is substantially isochronous, of the kind comprising complementary oscillating and nonoscillating partsinteracting magnetically to provide a modified total'restoring force by adding to or subtracting from the main restoring force, the oscillating part.v being apart of the oscillating mass, one of said parts' being shaped to present to the other part a relatively-divergent surface symmetrically throughout the amplitude of oscillation, mounting means for supporting. the non-oscillating part, and adjustablemeans for said mounting means for varying the-effective proximity of the said divergent surface to the other part, characterised in that the said divergent surface confronts the surface of the other part at the repose position of the oscillating part and has its divergent dimension at least equal to half the normal amplitude of oscillation and its radius of curvature not less than the normal maximum amplitude of oscillation.

2. A magnetic frequency regulator for an oscillating mass, having a non-magnetic main restoring force giving such mass a natural frequency of oscillation, of the kind comprising complementary oscillating and nonoscillating magnetically interacting parts, the oscillating part being a part of the oscillating mass, and the nonoscillating part being relatively stationary, means for adjusting the position of the stationary part to vary the magnetic interaction, one at least of said parts presenting to the other a convex face which is approximately normal to the repose axis of said arcuate path, such face being a substantially continuous face confronts the surface of the other part at the repose position of the oscillating part and having a radius of curvature between infinity and a radius equal to the normal amplitude of oscillation of the oscillating part and being of width at least equal to half the said normal amplitude, and the confronting face of the other part being of smaller width.

3. A magnetic frequency regulator for the oscillating mass of a timepiece, having a non-magnetic main restoring force giving such mass a natural frequency of oscillation which is substantially isochronous, of the kind comprising complementary oscillating and nonoscillating magnetically interacting parts, the oscillating part being a part of the oscillating mass, and the nonoscillating part being relatively stationary, means for adjusting the stationary part. towards and away from the said arcuate path, one at least of said parts presenting tothe other a convexface which isapproximately normal to the-repose axis of said arcuate path, such face being a substantially continuous face confronts the'surface ofthe other part at the repose position of the oscillating part and having a radius of curvature between infinity and a radius equal to the normal amplitude of oscillation of the oscillating part and being ofwidth at least equal to half thesaid normal amplitude, and the other face being of smaller width.

4. A magnetic frequency regulator for an oscillating mass, havinga non-magneticmainrestoring-force giving such mass a natural-frequency of oscillation, of the kind comprising complementary oscillating and nonoscillating magnetically interacting parts, the oscillating part being a part of the oscillating'mass,and the nonoscillating part being relatively stationary, means for adjusting the position of the stationary part to vary the magnetic interaction, one at'least of said parts" presenting to the other a convex face which isapproximately normal to the repose axis of said arcuate path, such face being a substantially continuous face confronting the surface of the other part atthe reposeposition of the oscillating part and having a radius ofcurvature between infinity'and a'radius equal to the normal'ampiitude ofoscillation of'theoscillating part and being of width at least equal to half the said normal amplitude, and the other face'being of smaller width, the modification of the main restoring force, obtainable from the magnetically interacting parts of the frequency regulator, being not moretha-n 10%.

5. A magnetic frequency regulator'f'or' the oscillating mass of a timepiece, having a non-magnetic main restoring force giving such mass a natural frequency of oscillation which is substantiallyisochronous, of the kind comprising complementary oscillating and nonoscillating mag netically interacting parts; the oscillating part being a part of the oscillating mass, and the nonoscillating part being relatively stationary, means for adjusting the stationary part towards and away from the said arcuate path, one at least ofsaid parts presenting to theother a convex face confronting the surface of the other part at the repose position of the oscillating part andwhich is approximately normal to the repose axis of said arcuate path, such face being a substantially continuous face having a radius of curvature between infinity and a radius equal to the normal amplitude of oscillation of the oscillating part and being of width at least equal to half said normal amplitude, and the other face being of smaller width, the second dimension of the convex face and the disposition of such face being such that it provides a full area of sweep relative to the other part.

6. A magnetic frequency regulator for the oscillating mass of a timepiece, having a non-magnetic main restoring force giving such mass a natural frequency of oscillation which is substantially isochronous, of the kind comprising complementary oscillating and nonoscillating magnetically interacting parts, the oscillating part being a part of the oscillating mass, and the nonoscillating part being relatively stationary, means for adjusting the stationary part towards and away from the said arcuate path, one at least of said parts presenting to the other a convex face which is approximately normal to the repose axis of said arcuate path, such face being a substantially continuous face having a radius of curvature between infinity and a radius equal to the normal amplitude of oscillation of the oscillating part and being of width at least equal to half said normal amplitude, and the other face being of smaller width, the means for adjusting the stationary part towards and away from the arcuate path comprising a cam and follower.

7. A magnetic frequency regulator according to claim 6 characterised in that the cam and follower are proportioned so that consecutive equal units of angular movement of the cam give resultant unequal units of movement of the adjustable part.

8. A magnetic frequency regulator according to claim 7, wherein the said equal and unequal units of movement are related in square root law, whereby equal movements of the regulator represent equal variation of frequency.

9. A magnetic frequency regulator for the oscillating mass of a timepiece, having a non-magnetic main restoring force giving such mass a natural frequency of oscillation which is substantially isochronous, of the kind comprising complementary oscillating and nonoscillating magnetically interacting parts, the oscillating part being a part of the oscillating mass, and the nonoscillating part being relatively stationary, means for adjusting the stationary part towards and away from the said arcuate path, one at least of said parts presenting to the other a convex face which is approximately normal to the repose axis of said arcuate path, such face being a substantially continuous face having a radius of curvature between infinity and a radius equal to the normal amplitude of oscillation of the oscillating part and being of width at least equal to half said normal amplitude, and the other face being of smaller width, the second dimension of the convex face and the disposition of such face being such that it provides a full area of sweep relative to the other part, and such that the second dimension varies symmetrically about the repose axis so as to modify the magnetic interaction throughout the oscillation.

10. A magnetic frequency regulator according to claim 9, characterised in that the variation of the second dimension is effected by forming an aperture within the swept area of the convex face.

11. A magnetic frequency regulator according to claim 3 in which the proximity adjustment provides movement of the stationary part in the direction of the axis of repose.

12. A magnetic frequency regulator according to claim 3 in which the proximity adjustment provides movement of the stationary part in the direction of the axis of repose of the oscillating part and to the plane of oscillation so that more or less of the area of the continuous face is within the magnetic field of the oscillating part.

13. A magnetic frequency compensator for an oscillating mass, having a main restoring force giving such mass a natural frequency of oscillation which is substantially isochronous, of the kind comprising complementary oscillating and nonoscillating parts interacting magnetically to provide a modified total restoring force by adding to or subtracting from the main restoring force, the oscillating part being a part of the oscillating mass, one of said parts being shaped to present to the other part a relatively divergent surface symmetrically throughout the amplitude of oscillation, mounting means for supporting the non-oscillating part, characterised in that the said divergent surface has its divergent dimension at least equal to half the normal amplitude of oscillation and its radius of curvature not less than the normal maximum amplitude of oscillation, whereby to provide isochronous compensation.

14. A compensating device for an oscillating mass having a nonmagnetic main restoring force for oscillating the mass at natural frequency, comprising fixed and movable complementary parts, respectively, of which the movable part is a part of the oscillating mass and one of said parts having a surface confronting the other part at least throughout the normal amplitude of oscillation of said mass and diverging from said other part in the repose position of said mass, and said parts interacting magnetically to produce a modified total restoring force by adding to or subtracting from the main restoring force.

15. A compensating device for an oscillating mass having a non-magnetic main restoring force for oscillating the mass at natural frequency, comprising fixed and movable complementary parts, respectively, of which the movable part is a part of the oscillating mass and one of said parts having a surface confronting the other part at least throughout the normal amplitude of oscillation of said mass and diverging from said other part in the repose position of said mass, and said parts interacting magnetically to add to the main restoring force at large amplitudes of oscillation of said mass.

References Cited in the file of this patent UNITED STATES PATENTS 1,825,382 Baker Sept. 29, 1931 2,571,085 Clifford Oct. 9, 1951 2,743,614 Clifford May 1, 1956 

